The Royal Navy's new aircraft carriers will reportedly be up against a new Russian missile that can travel at 4,000mph.
The Zircon, which could be operational next year, uses a "scramjet" engine to travel at five times the speed of sound, faster than a sniper's bullet.
Able to cover a distance of 155 miles in 2½ minutes, it is expected to be first fitted to a nuclear-powered Kirov-class warship, before being rolled out on Russia's strategic bombers and submarines.
According to the Times newspaper the missile will be too fast for current air-defence systems to cope with, despite the Royal Navy's new carriers being fitted with state-of-the-art anti-air defensive systems.
A Royal Navy spokesman, however, said: "We do not comment on force-protection measures but keep threats constantly under review."
The paper claims that the only current system capable of destroying such a missile is Russia's own S-500. The US is also developing hypersonic weapons but these are not thought to be close to even the production stage.
Russia, meanwhile, has hinted that the Zircon, which is expected to have a range of around 250 miles, could be tested this year.
While this range is shorter than some current Russian anti-ship weapons, with the warhead carrying conventional explosives, it's thought the impact of a missile striking a carrier at such speed would be "devastating".
The Zircon is able to travel at such speeds by using oxygen from the atmosphere rather than from a tank on board, thus allowing it to be smaller and lighter. In future, it's believed missiles will be able to travel at over 30 times the speed of sound.
It comes after claims the Royal Navy's ability to deploy its Astute hunter-killer submarines could be at risk because of delays in the construction of a dry dock to maintain them.
Construction of the dock is at least a year overdue, according to reports.
An MoD spokesperson said: "There is no delay. We continue to explore options for future submarine docking requirements at Devonport. No decisions have been taken and the Royal Navy’s ability to deploy Astute Class submarines remains unaffected."